Influence of Magnetostriction of NiFe Electroplated Film on the Noise of Fluxgate

Abstract

One of the sources of fluxgate noise is the noise originating in the magnetic core. Several parameters, such as anisotropy and shape, are traditionally studied and optimized to reduce the noise. In this paper, we show how the magnetostriction influences the noise of the fluxgate. We electroplated NiFe thin-film over a copper layer using different current density. By energy-dispersive X-ray spectroscopy we show that the mutual percentage of Fe and Ni in the film depends on the current density. As a result the magnetostriction is changed from negative to positive values, with minimum magnetostriction found at around Fe 19 Ni 81 composition. When we used these ring cores as base for a fluxgate we observed that the noise rapidly rises as the absolute value of magnetostriction increases, while the minimum noise is achieved at lowest value of magnetostriction. An increase of one order of magnitude of the magnetostriction causes and increment of almost two orders of magnitude in the noise. Therefore, we conclude that it is vital to employ alloys with the lowest possible magnetostriction as core for fluxgates.

Effect of Electroplated Ni1–xFexComposition on the Field-Induced Anisotropy

“…6 shows the value of the power spectral density of the noise at 1 Hz (commonly used as a reference value for magnetometers) vs. the current density used in electroplating. As we expected [9] the noise is lowest at current density j 0 =16 mA/cm 2 , where the Ni 0.81 Fe 0.19 composition is obtained, and the magnetostriction is the lowest, whereas the noise increases as we reduce or increase the current density and therefore increase the magnetostriction.…”

“…The current density was changed in order to change the composition of the electroplated film. Current density j 0 =16 mA/cm 2 returns an ideal Ni 0.81 Fe 0.19 composition, whereas if we increase j the content of iron will increase and vice versa if the current density is decreased the content of nickel increases [9]. In this paper we tested current density up to 3 times larger than j 0 and down to 0.5 times j 0 .…”

Magnetostriction Offset of Fluxgate Sensors

“…where M S is saturation magnetization evaluated from the B-H loop measured in the direction of applied stress. Technological details of the core preparation and technique to measure magnetostriction are described in [8].…”

Effect of Adjacent Interval Width on Noise Properties of Striped Array Iron Core Fluxgate

“…It has been reported that low-noise soft magnetic materials have a relatively low Curie temperature, minimal magnetostriction, and minimal eddy current loss. (10,11) Ni 81 Fe 19 and cobalt-based amorphous materials, which are low-noise soft magnetic materials, are usually preferred for preparing the iron cores of fluxgates. Although changing the fabrication process and annealing the soft magnetic material used can reduce the noise of fluxgates, these methods are not effective in reducing the noise of micro-fluxgates.…”